The synthesis of 5-oxo-2-pyrrolidinepropanoic acid then known as pyrrolidin-2-one-5-propanoic acid is reported in Chem. Ber., 88, 509 (1955). The synthesis of pyrrolidin-2-one-5-propanoic acid methyl ester is reported in J. Am. Chem. Soc., 69, 690 (1947). The synthesis of pyrrolidin-2-one-5-propanoic acid ethyl ester is reported in Coll. Czech. Chem. Comm., 12, 278 (1947). Pyrrolidin-2-one-5-propanoic acid amide is reported in Chem. Ber., 55B, 3950-3960 (1922) and the piperidide of pyrrolidin-2-one-5-propanoic acid is reported in Ann., 581, 225-237 (1953). The compounds are utilized in the references as chemical intermediates or as crystalline derivatives.